Engine control strategies may control fuel injection for combustion based on engine position. For example, engine position may be determined based on an angular position of one or more shafts of the engine, such as a camshaft or a crankshaft. The angular position of a shaft may be detected by a shaft position sensor configured to send a signal train indicative of position to a controller. In a particular example, an engine may include a fine resolution crankshaft having a crank wheel that includes sixty teeth that generates one hundred twenty edges each revolution. The engine further includes a coarse angular resolution camshaft having five targets that generate ten edges per camshaft revolution. The controller receives signal trains from the sensors based on detection of the teeth of the crankshaft and the targets of the camshaft and the controller time stamps and processes the signals of each signal train to determine the engine position.
At engine startup, in order to perform accurate fuel injection control for combustion, the controller and the engine position may be synchronized. Stated another way, engine position becomes known to the controller. In an example where engine position is determined based on signals from the camshaft position sensor, the engine may be cranked until the camshaft position sensor detects a reference marker, such as a cylinder identification (CID) of the camshaft. Upon detection of the CID, the controller may determine the position of the engine and may cause fuel injection to be performed for combustion at the next suitable engine position. Typically, the camshaft position sensor may detect the CID in approximately 270° to 740° of angular rotation of the camshaft or three edges of the camshaft targets to synchronize the engine position with the controller. It, it will be appreciated that a camshaft position sensor with multiple targets may be synchronized more quickly than those with single targets.
Fast engine startup may be desirable since a vehicle operator may perceive fast engine startup as an indication of vehicle reliability, among other things. For fast engine startup, minimal rotation of the camshaft to synchronize the controller and the engine position may be desired. In one approach, fast engine startup may be achieved by synchronizing the controller and the engine position based on the first identification of the CID (including camshaft position sensor systems with multiple targets per revolution) by the camshaft position sensor.
However, the inventor herein has recognized some issues with the above approach. In particular, in some cases, the first identification of the CID may be inaccurate resulting in the controller and the engine position being out of synchronization. Moreover, the lack of synchronization may lead to fuel injection control having reduced accuracy. Lack of synchronization between the controller and the engine position particularly may affect startup of a direct fuel injection engine. In particular, since fuel is injected directly into the cylinder, if the engine position known by the controller is inaccurate, fuel may be injected into the cylinder at an engine position that is inappropriate for combustion resulting in ineffective combustion or no combustion of the fuel. Thus, control of fuel injection with reduced accuracy as a result of the controller and the engine position being out of synchronization may result in ineffective combustion or no combustion which may lead to no-starts or miss-starts of the direct fuel injection engine. Moreover, no-starts and miss-starts as a result of the controller and engine position being out of synchronization may be more prevalent at cold temperatures due to slow shaft rotation, such as at a temperature less than 20° Fahrenheit.
At least some of the above issues may be overcome, in one approach, by a method of starting an engine, the engine including a cylinder and a fuel injector configured to directly inject fuel into the cylinder, the method comprising: at an engine start condition, receiving a sensed engine position; in response to the sensed engine position correlating with a stored engine stop position, injecting fuel directly into the cylinder at a next suitable engine position for a first combustion cycle; and in response to the sensed engine position not correlating with the stored engine stop position, rotating a shaft of the engine an angular distance without injecting fuel directly into the cylinder until the sensed engine position correlates with another parameter, and thereupon, injecting fuel directly into the cylinder at a next suitable engine position for a first combustion cycle.
In one example, a stored engine stop position is determined at the most recent engine shutdown. For example, a shaft position sensor may detect the shaft position and upon detection of a shaft of the engine reaching a standstill state the engine stop position may be determined based on the shaft position while taking into consideration reversals in shaft rotation during the course of engine shutdown in order to accurately determine the engine position. The determined engine stop position may be stored in memory and may be utilized at the subsequent engine startup.
By synchronizing the controller and the engine position based on a correlation between a sensed engine position and a stored engine stop position, confidence in the engine position may be improved for quick and accurate engine startup. In other words, the stored engine start position may be confirmed at the moment of receiving the first indication of the sensed engine position and fuel injection for engine startup may be performed with confidence. It will be appreciated that it may take three indications of shaft position (e.g., three camshaft target edges) to determine engine position, but it only takes one indication to confirm the stored engine stop position as being the actual engine position. With each subsequent indication of sensed shaft position, the engine stop position may further be confirmed.
Furthermore, in the event that the sensed engine position and the stored engine stop position (incremented as crankshaft displacement is sensed) are not correlated, fuel injection may be delayed in order to increase the confidence in the engine position by rotating the shaft to determine a additional indications of the sensed engine position that may correlate with another parameter. For example, the additional indication of the sensed engine position may correlate with the stored engine stop position and fuel injection may be performed. As another example, the stored engine stop position may be dismissed and the shaft may be rotated further in order to repeatedly detect a sensed engine position and fuel injection may be performed based on the correlation with the repeated detection of the sensed engine position. By delaying fuel injection in order to determine the engine position with confidence, the likelihood of no-starts and miss-starts may be reduced and difficult restarts may be virtually avoided. In this way, engine startup may be made more robust.